Metal molybdite catalyzed dehydration process



Patented Apr. 1, 1952 METAL MOLYBDITE OATALYZED DEHYDRATION PROCESS Herrick E. Arnold, Wilmington, and James E. Carnahan, New Castle, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application February 9, 1950, i 4

Serial No. 143,351

13 Claims. 1

This invention relates to dehydration processes and more particularly to a novel catalytic dehydration process.

This application is a continuation-in-part of our copending application Serial No. 111,982, filed August 23, 1949, now Patent No. 2,572,300.

Organic compounds capable of undergoing dehydration reactions, such as alcohols, have heretofore been subjected to dehydration reactions in the presence of various anhydrous metal oxide catalysts. The anhydrous metal oxides constitute an important class of catalysts and are classified according to their eifect on alcohols as dehydrogenating, dehydrating, or mixed dehydrogenating-dehydrating catalysts. Oxides of aluminum and of silicon have heretofore been used as catalysts in dehydration processes.

It is an object of this invention to provide a novel catalytic dehydration process. A further object is to provide an improved catalytic process for dehydrating organic compounds capable of undergoing dehydration. A still further object is to provide a catalytic dehydration process of broad applicability which employs a rugged and highly selective catalyst. Other objects will appear hereinafter.

This invention provides a dehydration process which comprises contacting an organic compound capable of undergoing dehydration with a molybdite of a metal whose ions are soluble in excess aqueous ammonia; that is whose ions are soluble in aqueous ammonia in amount greater than that stoichiometrically required to precipitate the metal ion. These catalysts are metal molybdites whose ions are not precipitated as insoluble oxides or hydroxides'when solutions of their salts are treated with aqueous ammonia in amount slightly in excess of that which is theoretically required for the formation of the metal oxide or hydroxide. Accordingly this invention provides an improved dehydration process, the improvement residing in effecting the dehydration reaction in the presence of a metal molybdite whose ions are not precipitated as insoluble oxides or hydroxides when solutions of its salts ar treated with aqueous ammonia in off-gases were vented through a meter.

2 cision fractional distillation or other means known to those skilled in the art.

The examples which follow illustrate specific preferred embodiments of the invention and are not to be construed as limitations thereof.

Example I A heat-resistant glass reactor mounted in a vertical electric furnace was packed with 100 ml. of 8-14 mesh zinc molybdite catalyst, prepared as described subsequently. With the catalyst at 345 i 3C. and under atmospheric pressure, 100 g. (0.77 mol) of octanol-2 was vaporized and fed at constant rate into the reactor during a period of 4.9 hours, along with a stream of nitrogen flowing at the rate of 0.05 liter per minute. The calculated contact time was 26 seconds. Exit gases from the reactor were received and cooled in a series of condensers operating at decreasing temperatures to C. and the uncondensible Fractional distillation of the condensate showed that the product was a mixture of octenes which had formed in 82% conversion. Infrared spectroanalysis indicated that 4% of the product was l-octene, while the remainder consisted of the other isomeric linear octenes.

The catalyst was prepared as follows:

Five liters of a 2 molar aqueous solution of ammonium molybdate was added to an equal volume of a 2 molar aqueous solution of zinc nitrate and the pH of the resulting slurry adjusted to 7 by addition of 670 cc. of 28% aqueous ammonia. The precipitated zinc aminomolybdate (ZHMOO4.NH3.H20) was washed with distilled, water, filtered, dried and then calcined at 400 C. The calcination step converted the zinc aminomolybdate to the normal zinc molybdate The normal zinc molybdate thus obtained was converted to zinc molybdite by reduction in hydrogen by stepwise temperature increments starting at 200 C. and carried to 550 C. during a total period of 27.5 hours of which time 21 hours were at 550 C. The reaction was as follows:

ZnMoOr+Hz- ZnMoOs'+I-Iz0 The zinc molybdite was essentially insoluble in 10% hydrochloric acid and in 28% ammonia, whereas the zinc aminomolybdate and zinc molybdate were almost completely soluble in these solvents. The reaction of the zinc molybdate to zinc molybdite also produced a ten-fold increase in surface area. as shown below:

1 Measurements were made according to the procedure described in a paper by P. H. Emmett, entitled A New Method for Measuring the Surface Areas oi Finely Divided Materials and for Determining the Size of Particles, Am. Soc. for Testing Materials, March 4, 1941, Symposium on NewMethods for Particle Size Determination in the Sub-Sieve Range.

X-ray diffraction analysis of the zinc molybdite indicated that this material had the characteristic system of lines corresponding to a. single cubic structure. Analysis of the zinc molybdite indicated it to contain an average of 31.9 Zn and 44.8% molybdenum. The calculated values for ZnMoOa are 31.2% -Zn and 45.4% Mo.

Example TI Example I was repeated using tert.'-butanol as the reactant. The catalyst, 50 ml. in volume, was maintained at 310:10 C. under atmospheric pressure while 37 g. (0.5 mole) of tert.-butanol was vaporized at a constant rate during 1.? hours and fed into the reactorthrough which nitrogen was flowing at the rate of 0.1 liter per minute. The calculated contact time was 7 seconds. Distillation of the exit gases which were'collected in a receiver at -80 C. gave isobutylene in substantially quantitative conversion. When the temperature of the catalystwas reduced to 175 :5 0., the corresponding conversion was 13%.

Example III Example 1V During a period of 2.1 hours,actic acid -(60 g. or 1.0 mole) and ammonia gas (2.1-mole) were fed simultaneously under atmospheric pressure and at constant rates into a-reactor containing 100 ml. of zinc molybdite catalyst prepared as described in Example I. The temperature of the reactor was maintained at 405x20 C. and hydrogen flowing at 0.6 liter per minute was employed as a sweep gas. 4 seconds. traps, the first cooled at C. and the second to -80 C. The combined product from both traps was in two layers. The upper layer was separated, dried, and distilled. Acetonitrile was obtained in 54% conversion.

Example V A mixture of 75g. of t-amyl alcohol and 2.5 g. of nickel molybdite catalyst, prepared by a methheated to reflux (B. P. 102 C.) under a fractionating column at atmospheric pressure. Distillate amounting to 15 g. was collected in the boiling range 35 to 42 C., N 1.3809. The distillate K 75 lower pressures than atmospheric in order to in,-

was dried over sodium sulfate and'on're distilla- The calculated contact time was The exit gases were collected in two 00 tion the bulk of the material distilled at 34 to 37 C. The distilled product was characterized by infrared analysis to be a mixture of 2-methyl-1- butene and 2-methyl-2-butene.

In the foregoing examples certain preferred conditions of temperature, space velocity, contact time, catalyst volume, pressure, etc., have been used. It is to be understood, however, that these values can be varied within the scope of this invention without affecting its utility.

By the process of this invention any intramolecular or intermolecular dehydration can be efiected advantageously.

Intramolecular dehydrations are reactions in- 'volving a molecule of one substance to form water as one of the products of reaction. Typical of such reactions are the formation of hydrocarbons from monohydric alcohols, the formation of cyclic ethers from polyhydric alcohols, the production of simple cyclic acid anhydrides from dicarboxylic acids, and the production of hydrocarbons from cyclic ethers.

Intermolecular dehydrations are reactions involving two or more reacting molecules to form 5 wateras one of the products of reaction. Exemplary of such reactions are "the formation of acyclic ethers from alcohols, or open-chainanhydrides from monocarboxylic acids formation of nitriles from carboxylic acid substances and 0 ammonia, production of heterocyclic nitrogen compounds from ammonia'oramines and either aldehydes or ketones, theproduction of "amines from alcohols and either ammonia or primary or secondary amines, and-the like. Operable compounds for use in the process of this invention are those containing an oxy or 0x0 group as exemplifiedby alcohols, such methyl alcohol, propyl alcohol, octyl alcohol, dodecyl alcohol,'octadecyl alcohol, and the like; ethylene glycol, butyleneglycol, and the likeycyclohexanoL'and the like; acidssuch as acetic acid, propionic acid, caproic acid, capric acid. dode- 'canoic acid, octa'decanoic acid, and the like; maleic acid, phthalic acid;ben'zoic acid, cyclohexane carboxylic acid, toluicacid,-naphthoic acid, and

4 the like; ethers such as diethyl etherpdipropyl ether,'propyl amyl'ether, tetrahydrofurane, and the like; aldehydes and ketonessuch as paraldehyde, acetaldeh'yde, propionaldehyde, butyraldehyde, 'octanal-l, dodecanol-l, acetone, methyl ethyl ketone, 'diamyl ketone, hexyl decyl ketone,

and the like.

The dehydration may be conducted with the oxy or oxo compound assole reactants or' it may be conducted in tlie presence of another material capable of reacting with the oxy or oxo compound with the elimination of Water. Examples'ofsuch other reactantare ammonia, primary and secondary amines such 5 as methyl amine, butyl amine, octyl amine,-dodecyl aminefdibutyl amine, butyl-decyl am'ine, dioctylamine, didodecyl amine,

and 'sulfhydryl compounds suchashydroge'n sol-- fide or mercapta'ns and the like.

Broadly speaking the process or this invention is operable within the'temperature range of from 50 to 50050. It is preferred, however, to utilize "temperatures in the range of 90 to 450 C. be-

cause within thismore restricted temperature range the majority of the, reactants utilized in od analogous to that described inExample I, was h Process the inventmn mp1ete1y "volatile.

The process of this invention is preferably practiced at ordinary pressures, although nodisadvantages occur when it is operated at higher or T. crease-the capacity .of a givemunit o-apparatuet or to facilitate vaporization-=01. high boiling re..-.;. actants."

Incontinuous operation; the contaettime, which is the time inseconds; required by the reactants to traverse the entire 'VOIUIHQDithBCatalyst space at the temperature and pressure em ployed, is an important variable.- The time :of 1 contact is not'only dependent-on the temperature and pressure but also on the-catalystvolume andfeed rate.- In the practice ofthisinvention these. important interdependentvariables --are--adjustedso-that the contact time-is within the-range of -1 to 100 seconds and preferably within from-2 to- 50" seconds.

The catalysts used in-the'practice of this invention are the metal molybditesdisclosed and claimed in our copending applicatiom serial No.- 11l,982 filed 'August 23, 1949,0f which the present application is a continuation-in-parta These molybdites exist in two'series; in the first 'of" which the molybdenum-is present in-the;quad-" rivalent state corresponding to the 'oxide-MoOa and the hypothetical acid I-IzMoOa', while inthe second series the molybdenum exists in the bivalent state corresponding to the oxide M00 and the hypothetical acid-HzMoOz. These molybdites may contain promoters or modifiers, such as iron, cadmium, barium, chromium, thorium, cobalt, copper, andthe like, if desired Preferred molybdites because of their high degreeof activity. are zinc molybdite having the formulaZnMoOa, nicke1 molybydite having the formula NiMOOz, cobalt molybdite having formulas corresponding, to COMOOz and COMOOs manganese molybdite. and copper molybdite having the formula CUMOQa. These molybdites are preferably used in the form of pellets in stationary-bed continuous-fiow'reactors in order to minimize mechanical losses of catalyst. In moving-bed continuous-flow reactors or in refluxing liquids, the catalyst is more advantageously employed in finely divided form.

The amount of catalyst employed in a specific operation depends upon such interdependent variables as temperature, contact time, pressure, particular catalyst, and the like. As a rule, in continuous operation the quantity of catalyst employed should be adjusted to yield a contact time of 1 to 25 seconds. In batch operation at least 0.01% by weight of catalyst, based on the weight of the material being processed, is employed. The use of amounts in excess of 25% of catalyst, based on the weight of the material or materials being processed, has no practical advantage and this value therefore represents the economic upper limit of catalyst ratio.

When the activity of the catalyst decreases or disappears through prolonged use, it may be restored by oxidizing the spent molybdite in air or oxygen at temperatures up to 500 C. and then reducing the resulting molybdate back to molybdite by the procedure illustrated in Example I.

The use of an added reaction medium is not essential but its employment is sometimes desirable to aid in the dissipation of the heat of reaction. AS reaction media for vapor-phase operations, there may be used inert gases such as nitrogen or normally liquid, volatile, organic solvents, such as isooctane, cyclohexane, and benzene. In liquid phase operations hydrocarbons, such as benzene, xylenes or mineral oils can be employed as reaction media.

The process of this invention is advantageous over the use of chemical dehydrating agents becausenmauxiliany chemicals .are .employed.- This; is: especially: .desirablel fromthe economic stands; point. Moreover, the process doesnotinvolve the;

handling of. corrosive dehydrating. .agentslsuch asphosphorus :pentachloride. sulfuric. acid, and

the like The processis particularly useful for synthesizing nitriles from: amides-.or ammonium. salts,,.or from ammonia and 'carboxylic. acids. Inrsuch syntheses the-amount of undesirableby-products to operate in a an 1 atmosphere .of ammonia and thus minimize the-formation of tarry products.

andother undesiredmaterials.- Convenient ammonia: acid ratios are between-2:1'and--15:1. Nitrile's which are advantageously -prepared by the process of this inventionare those of-acetic, capric, lauric, myristic, palmitic,- oleic, linoleic, I

adipic, sebacic, phthalic, andbenzoic acids.

Amines can be prepared in good yields bythe direct amination of-alcohols.- In such aminations the -molecular ratio of alcoholzammonia is theimportant variable influencing yield and proportionpf primary, secondary, and tertiary amines in the product; At low alcohol: ammonia ratios,-

eg, 1 :4 primary amine is the principal product while at a ratio of 3:1 primary amine essentially; disappears; the products consisting primarily of secondary and tertiary amines, the latterbeingformed in the largestamountg Heterocyclic nitrogen compounds can be ad vantageously prepared by the process of this invention. Thus, picolines andpollidines canbe advantageously made from ammonia and either aldehydes or ketones.

The cleavage of tetrahydrofuran to butadiene can be readily effected and for this reaction the process is highly useful.

As many apparently widely difierent embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims. I

We claim:

1. In a process for catalytically abstracting water from organic compounds capable of undergoing dehydration, the improvement which comprises contacting an organic compound capable of undergoing dehydration and selected from the class consisting of organic compounds containing an oxo group, organic compounds containing an oxy group and organic compounds containing a carboxylic acid group, at a temperature of 50 to 00 C. with a molybdite of a metal whose ions are soluble in aqueous ammonia in amount greater than that stoichiometrically required to precipitate the metal ion, said metal molybdite being a metal salt of an acid having one of the formulas corresponding to H2M0O2 and H2MOO3.

2. In a process as set forth in claim 1 wherein said metal molybdite is zinc molybdite having the formula ZnMoOa.

3. In a process as set forth in claim 1 wherein said metal molybdite is nickel molybdite having the formula NiMOOz.

4. In a process as set forth in claim 1 wherein said organic compound is vaporized and said metal molybdite is contacted with the vaporized organic compound at a temperature of to 450 C.

5. In a process as set forth in claim 1 wherein 7 said metal molybdite is contacted with said organic compound in liquid phase at a temperature of 90 to 450 C.

'6. In a process for the dehydration of an alcohol capable of undergoing dehydration, the improvement which comprises contacting said alcohol at a temperature of 50 to 500 C. with a molybdite of a metal whose ions are soluble in aqueous ammonia in amount greater than that stoichiometrically required to precipitate the metal ion, said metal molybdite being a metal salt of an acid having one of the formulas corresponding to HzMooz and HzMOO-a.

'I. In a process for the dehydration of an alkanol to an alkene, the improvement which comprises contacting said alkanol at a temperature of 90 to 450 C. with zinc molybdite having the formula ZnMoOa.

8. In a process for the dehydration of an alkanol to an alkene, the improvement which comprises contacting said alkanol at a temperature of 90 to 450 C. with nickel molybdite having the formula NiMooz.

9. In a process for the dehydration of a carboxylic acid and ammonia to form the nitrile of said acid, the improvement which comprises contacting said carboxylic acid and ammonia at a temperature of 50 to 500 C. with a molybdite of a metal whose ions are soluble in aqueous ammonia in amount greater than that stoichiometrically required to precipitate the metal ion, said metal molybdite being a metal salt of an acid having one of the formulas corresponding to H2M002 and HzMOOs.

10. In a process for the dehydration of a carboxylic acid and ammonia to form the nitrile of said acid, the improvement which comprises contacting said carboxylic acid and ammonia at 8. a temperature of 90 to 450 C. with zinc molyb dite having the formula 211M003.

11. In a process for the dehydration of a carboxylic acid and ammonia to form the nitrile of said acid, the improvement which comprises contacting said carboxylic acid and ammonia at a temperature of 90 to 450 C. with nickel molybdite having the formula NiMoOz.

12. In a process for the dehydration of acetic acid and ammonia to form acetonitrile, the improvement which comprises contacting said acetic acid and ammonia at a temperature of 90 to 450 C. with zinc molybdite having the formula ZnMoOa.

13. In a process for the dehydration of acetic acid and ammonia to form acetonitrile, the improvemnt which comprises contacting said acetic -acid and ammonia at a temperature of 90 to 450 C. with a molybdite of a metal whose ions are soluble in aqueous ammonia in amount greater than that stoichiometrically required to precipitate the metal ion, said metal molybdite being a metal salt of an acid having one of the formulas corresponding to HzMoOz and I-IzMoOa.

HERRICK R. ARNOLD. JAMES E. CARNAI-IAN.

REFERENCES CITED The following references are of record in the file of this. patent:

UNITED STATES PATENTS 

1. IN A PROCESS FOR CATALYTICALLY ABSTRACTING WATER FROM ORGANIC COMPOUNDS CAPABLE OF UNDERGOING DEHYDRATION, THE IMPROVEMENT WHICH COMPRISES CONTACTING AN ORGANIC COMPOUND CAPABLE OF UNDERGOING DEHYDRATION AND SELECTED FROM THE CLASS CONSISTING OF ORGANIC COMPOUNDS CONTAINING AN OXO GROUP, ORGANIC COMPOUNDS CONTAINING AN OXY GROUP AND ORGANIC COMPOUNDS CONTAINING A CARBOXYLIC ACID GROUP, AT A TEMPERATURE OF 50* TO 500* C. WITH A MOLYBDITE OF A METAL WHOSE IONS ARE SOLUBLE IN AQUEOUS AMMONIA IN AMOUNT GREATER THAN THAT STOICHIOMETRICALLY REQUIRED TO PRECIPITATE THE METAL ION, SAID METAL MOLYBDITE BEING A METAL SALT OF AN ACID HAVING ONE OF THE FORMULAS CORRESPONDING TO H2MO02 AND H2MO03. 